This invention relates to gauges for measuring the temperature or pressure of fluids, such as liquids or gases. More particularly, the invention relates to an improved gauge pointer that causes substantial drag when operated in a liquid making the pointer dynamically stable in a liquid filled temperature or pressure gauge. The improved gauge pointer is suitable for a gauge environment having substantial vibration or pressure fluctuation.
Although the invention is suitable for use with both temperature and pressure gauges, for purposes of illustration, this description principally concentrates pressure gauges. For the most part, the advantages and features of the invention are the same, whether used in temperature or pressure gauges.
The most common kind of pressure gauge employed in the prior art uses a "Bourdon Tube" for sensing variations in pressure. Traditionally, such Bourdon Tube pressure gauges employ a hollow tube having a generally elliptical cross section. The tube is closed at one end and is most often formed in the shape of a "C". The tube's open end is connected to the fluid to be measured, which flows into the Bourdon Tube through the open end, filling the "C". Higher pressure liquids tend to unbend the tube, which increases the radius of the "C" and results in curvilinear displacement of the closed end of the tube in a generally radial direction in the plane of the "C" and with respect to the center of the "C". A linkage mechanism is normally attached to the closed end of the Bourdon Tube "C", translating the linear displacement of the tube end, usually through a rack and pinion or related mechansim, to a gauge pointer. The gauge pointer rotates in response to the linear motion of the closed end of the Bourdon Tube and, when properly calibrated, indicates a pressure reading on a circular dial. Bourdon Tube pressure gauges of the kind described above have long been used and are well-known in the prior art.
Temperature gauges operate in a somewhat similar manner, although temperature gauges are usually not constructed with a Bourdon Tube. Generally, a gauge pointer, adapted for rotational movement to indicate temperature on a circular dial, is attached to a gear mechanism. The gear mechanism is in turn attached to a linearly moving element that is responsive to temperature changes, thereby producing corresponding gauge readings
Pressure and temperature gauges of all configurations, including Bourdon Tube pressure gauges, suffer from decreased effectiveness in fluid environments having substantial vibration of the gauge or frequent fluctuations or pulsations in pressure. Vibration is usually transmitted throughout the gauge by the direct mechanical connection of the gauge components, resulting in an increase in the stress on the pressure or temperature gauge components that act to reduce the effective life of the gauge. Similarly, vibration and pressure fluctuation or pulsation, especially in pressure gauges, can cause the gauge pointer to "flutter", that is, rapidly fluctuate about an approximate pressure or temperature reading. Such pointer flutter is both annoying to individuals attempting to read the gauge and detrimental to accurate pressure measurements.
To counteract the adverse effects of pressure pulsation or gauge vibration, a variety of different techniques have been adopted in the prior art, especially for pressure gauges. Various Bourdon Tube configurations other than a "C" tube have been tried, including pressure responsive tubes wound in a spiral fashion, and helically expanding tubes, commonly known as "pig tails". In some prior art configurations, the Bourdon Tube has been replaced with a diaphragm or bellows mechanism, usually consisting of a single or plural layer membrane that has at least one surface that moves upon pressure changes. Movement of the diaphragm or bellows result in a linear motion that is translated through a system of gears or other mechanical components to a rotating gauge pointer. In almost every pressure gauge, whether it has a Bourdon Tube or is constructed in one of the other manners described above, the motion responsive mechanism is attached through a direct mechanical connection to the pointer, which indicates pressure on a flat and usually cylindrical dial.
To counteract the undesirable effects of vibration, pulsation or pressure fluctuation, modern pressure or temperature gauges are usually filled with a liquid that acts as a damper. The liquid is often a clear, dense viscous material, such as glycerin or silicone. The entire gauge is then filled with the liquid which then acts to restrain or cushion the movement of all components, including the tube or diaphragm, the gear mechanism, and the pointer. Use of a liquid damping agent tends to improve service life of the pressure or temperature gauge components and usually reduces pointer flutter to thereby improve the ease of reading temperature or pressure. Additionally pressure fluctuation or pulsation can be often corrected or minimized by adding a pulsation damper, such as a porous metalic filter, over the entrance to the pressure sensing device (such as the Bourdon Tube or diaphragm). Pulsation damping can also be reduced by installing and using a screw opening leading to the oriface, or through use of an adjustable needle-type filter valve leading to the oriface. Each of these configurations are well known in the art.
While such techniques and constructions are often adequate to eliminate several of the undesirable effects of pressure fluctuation or pulsation, they have little, if any, effect on direct gauge vibration problems. Typically, vibration of the gauge elements (including the pointer) is produced by the vibrational movement of the device or apparatus upon which the gauge is mounted, and is directly transmitted to the gauge body through the mechanical connection of the gauge to that device, rather than through the fluid being measured. For example, a pressure gauge mounted on a liquid compressor will often encounter substantial pointer flutter and corresponding component wear, because the reciprocating or related movement of the compressor is directly transferred to the gauge mount, and hence, to its internal components. To eliminate such vibration problems, temperature and pressure gauges in the prior art were often mounted on a stable platform positioned away from the source of vibration (that is, away from the vibrating machine). The fluid source was then usually connected through a series of pipes or capillary tubes to the position of the pressure or temperature gauge. While this method effectively eliminates problems associated with direct vibration, it often results in substantial inconvenience to the equipment operator, who must move away from the machine to read the temperature or pressure gauge. The need for additional piping and piping support has also added further expense to prior art pressure or temperature monitoring systems. The problems of pressure fluctuation, pulsation and vibration have therefore not been fully resolved by the solutions disclosed in the prior art, and direct drive pressure and temperature indicators still suffer from wear and the inaccuracy associated with pointer flutter.
Accordingly, it is an object of this invention to provide an improved gauge mechanism for the measurement of fluid pressure or temperature.
It is a further object of this invention to provide an improved gauge mechanism that extends the life of gauge mechanical components by reducing the wear and related stress that usually results from pressure fluctuation or pulsation, or from gauge vibration.
Another object of this invention is to provide a pressure or temperature gauge mechanism capable of providing precise gauge readings without pointer flutter.
A further object of this invention is to provide a pointer for use in a liquid filled pressure or temperature gauge that dynamically resists pointer flutter resulting from gauge vibration, or pressure fluctuation or pulsation.
An additional object of this invention is to provide an improved flutter resistant pointer that can be used with existing liquid filled temperature or pressure gauges.
Yet another object of this invention is to provide an improved pointer for a liquid filled pressure or temperature gauge mechanism that is efficient and economical to manufacture.
Still another object of this invention is to provide an improved pointer for a liquid filled pressure or temperature gauge mechanism that can be constructed as a modification to the configuration of existing gauge pointers.